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  1. lucky6969b

    A question on the voltage level at the circled node

    Consider the voltage level at the circled node, if that voltage level is calculated by the Kirchhoffs voltage law (summing from the 5V rail to the 0V rail) , but if the node is also connected to the chip, we don't know what components are available inside that chip, can we assume the voltage...
  2. lucky6969b

    How does the current mirror work?

    Okay, I remember now. The current of a transistor circuit doesn't depend on the DC voltage, but the base current/voltage. So the Ic doesn't depend on Rc. Right? - - - Updated - - - Ok, get it, the potential difference all over is 18V with a 0.65V transistor difference. divided by Rc...
  3. lucky6969b

    How does the current mirror work?

    Thanks, I understand some of the parts now. The transistor is acting like a diode, but 18V - 0.65V, if the 0.65V is he drop across the transistor, but why not considered Rc which might have a resistance of several Kilo ohms or Mega on its own. if so, the voltage drop across it might be ~17V...
  4. lucky6969b

    How does the current mirror work?

    No voltage drop across T1? Sorry, I am quite new to current mirror circuit Why not IcRc + Ic(Resistance of transistor 1) = 18V 18V / Rc + Resistance of transistor 1) = Ic
  5. lucky6969b

    How does the current mirror work?

    Is the reference point right at the middle of T1 and Rc, I mean how do you get 18V - 0.65V Counting from the collector of T1? Thank
  6. lucky6969b

    How does the current mirror work?

    I don't know if we are referring to nodal analysis here. Where is the reference point? Thanks
  7. lucky6969b

    How does the current mirror work?

    https://en.wikipedia.org/wiki/Current_mirror I don't understand if the positive rail is +9V and negative rail is -9V Why the current is 18V - 0.65V / Rc? Anyone explain this? Thanks Jack
  8. lucky6969b

    Capacitor DC charging question.

    Sorry, I have come back. In physics, I remember there is one thing called displacement current, where energy stored in magnetic fields are transformed into electric fields in between the cap and transformed back into magnetic fields on the other side of the cap for continuous currents. So my...
  9. lucky6969b

    Power Supply Question

    I mean how come a 13A mains can supply enough energy to both a 520W and 500W supply or even 1000W? as the energy supplied is finite. Thanks Jack
  10. lucky6969b

    Power Supply Question

    I have a 520W power supply for my personal computer appliances. I used to have a 500W power supply for the the same computer set. If the mains supplies 13A of current, would the 520W power supply draw more energy than the 500W one from the mains to the supply, meanwhile the current is constant...
  11. lucky6969b

    How do you go about troubleshooting a resistor on a PCB?

    For instance, to check it if it has blown out. Bad resistors do have infinite resistance or shorted sometimes, right?
  12. lucky6969b

    How do you go about troubleshooting a resistor on a PCB?

    Does it have a polarity? How can you tell which side is positive and the other side is negative? Thanks Jack
  13. lucky6969b

    Capacitor DC charging question.

    Positive varying voltages/currents in the first half of the cycle and non-varying second half are also called DC? That's what it is called pulsating? Thanks Jack
  14. lucky6969b

    Capacitor DC charging question.

    We can't say a sinusoidal waveform has a fundamental frequency of 0Hz because the lowest frequency is 0, it's DC? Right? Thanks Jack
  15. lucky6969b

    Capacitor DC charging question.

    Maybe a link to read? I think it's better to think of it in physics perspective.
  16. lucky6969b

    Capacitor DC charging question.

    I just read my physics book today, something is related to the capacitor - The displacement current. How does it relate to the operation of a capacitor? Thanks Jack
  17. lucky6969b

    Capacitor DC charging question.

    During the positive cycle, the capacitor will get charged. However, ac current will flow through the cap rather than establishing potential difference between the plates. All the energy should be "dissipated" during that time. That's what I don't understand.
  18. lucky6969b

    Capacitor DC charging question.

    In this circuit during the first cycle, the capacitor is charged up, but there isn't any DC component in the source. How come will there be smoothing out effects on the load? Thanks Jack
  19. lucky6969b

    Book recommendations for analysing complex circuits

    Could anyone please recommend some books on such topic? Some circuits may contain a lot of nodes and branches in various configurations. Elementary books just introduce circuit elements and signals etc and not touching the subject of figuring out how complex networks work... Thanks Jack

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